Q. Are we allowed to swear by the Qur’aan or any other attribute of Allaah?
A.The shaykh (hafidahullaah) said, swearing by any of the attributes of Allaah such as, Ar-Rahmaan or any other attribute of Allaah or swearing by the Qur’aan which is one of the attributes of Allaah, there is no problem with this. However, it is best to swear just by the names of Allaah so that no doubt or no confusion or misunderstanding is involved. The names of Allaah are plenty. There are plenty of names that we can swear by and there are not only a hundred. There are more than a hundred names. We know there is a narration talking about the ninety nine names of Allaah azza wa jall but there are more than a hundred names of Allaah azza wa jall and it is permissible to swear by any of them.
Shaykh Saalih Muhammad al-Luhaydaan (May Allaah preserve him) (Kitaab-ut-Tawheed Class, Q&A Session 08-08-2012, Riyadh)